Lidar receiving apparatus, lidar system and laser ranging method

ABSTRACT

The present application provides a lidar receiving apparatus, a lidar system, a laser ranging method, a laser ranging controller, and a computer readable storage medium. The lidar receiving apparatus includes: a photodetector, which is configured to receive a reflected laser signal and to convert the reflected laser signal into a current signal when a bias voltage of the photodetector is greater than a breakdown voltage of the same; a ranging circuit, which is connected with the photodetector and configured to calculate distance data according to the current signal; and a power control circuit, which is connected with the photodetector and configured to control the bias voltage applied to the photodetector according to a predefined rule.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 17/264,544 filed on Jan. 29, 2021, which is a national stage ofInternational Application No. PCT/CN2020/080350, filed on Mar. 20, 2020,which claims the benefit of priority to China Patent Application No.201910576631.0, filed on Jun. 28, 2019, the content of which areincorporated herein by references in their entireties.

TECHNICAL FIELD

The present application relates to the field of lidar technology, andparticularly to a lidar receiving apparatus, a lidar system, a laserranging method, a laser ranging controller and a computer readablestorage medium.

BACKGROUND

A lidar system is increasingly applied to application scenarios such asautonomous driving.

However, in a lidar system, due to optical design limitations,transmitted light (laser signal) may be directly reflected to a receivervia the inner wall of a lens barrel or via impurities on the lens,forming a false reflected signal. For a photodetector with a relativelylong recovery time, no real echo may be observed for a time periodthereafter, and there will be a certain range of blind areas.

However, it is difficult for a traditional lidar to solve theabove-mentioned problem of the short-range blind areas.

SUMMARY

Accordingly, it is necessary to provide a lidar receiving apparatus, alidar system, a laser ranging method, a laser ranging controller and acomputer readable storage medium capable of decreasing a short-rangeblind area in view of the above technical problems.

In a first aspect, a lidar receiving apparatus includes:

-   -   a photodetector, which is configured to receive a reflected        laser signal, and to convert the reflected laser signal into a        current signal when a bias voltage of the photodetector is        greater than a breakdown voltage of the same;    -   a ranging circuit, which is connected with the photodetector,        and configured to calculate distance data according to the        current signal;    -   a power control circuit, which is connected with the        photodetector, and configured to control the bias voltage        applied to the photodetector according to a predefined rule;    -   wherein the predefined rule includes: at a receiving time of a        stray reflected signal, the bias voltage of the photodetector is        smaller than the breakdown voltage; and the receiving time of        the stray reflected signal is a time at which a transmitted        laser signal reaches the photodetector through a stray light        path other than a ranging light path, and is correlated to a        preset flight time of the stray reflected signal.

In one embodiment, the ranging circuit includes:

-   -   a trans-impedance amplifying circuit, which is connected with        the photodetector, and configured to convert the current signal        into a voltage signal and amplify the voltage signal to acquire        an amplified voltage signal; and    -   a first processing circuit, which is connected with the        trans-impedance amplifying circuit, and configured to control        the bias voltage applied to the photodetector according to the        predefined rule, and calculate distance data according to the        amplified voltage signal.

In one embodiment, the lidar receiving apparatus further includes areference photodetector, wherein the reference photodetector is in alight-shielded state, and is connected in parallel with thephotodetector;

-   -   the ranging circuit includes:    -   a cancelling and trans-impedance amplifying circuit, which is        connected with the photodetector and the reference        photodetector, respectively, and configured to perform        cancellation and trans-impedance amplification on both current        signals output from the photodetector and the reference        photodetector and output voltage signals obtained after the        cancellation and the trans-impedance amplification are        performed, wherein the current signal output from the reference        photodetector is positively correlated to the bias voltage        applied to the reference photodetector; and    -   a second processing circuit, which is connected with the        cancelling and trans-impedance amplifying circuit, and        configured to control the bias voltage applied to the        photodetector according to the predefined rule and calculate the        distance data according to the voltage signal obtained after the        cancellation and the trans-impedance amplification are        performed.

In one embodiment, the cancelling and trans-impedance amplifying circuitincludes:

-   -   a first cancelling circuit, which is connected with the        photodetector and the reference photodetector, respectively, and        configured to cancel both current signals output from the        photodetector and the reference photodetector and output        cancelled current signals;    -   a first trans-impedance amplifying circuit, which is connected        with the first cancelling circuit, and configured to convert the        cancelled current signals into voltage signals and amplify the        voltage signals to acquire amplified voltage signals.

In one embodiment, the cancelling and trans-impedance amplifying circuitincludes:

-   -   a second trans-impedance amplifying circuit, which is connected        with the photodetector and the reference photodetector,        respectively, and configured to convert both current signals        output from the photodetector and the reference photodetector        into voltage signals, respectively, and amplify the voltage        signals to acquire two amplified voltage signals; and    -   a second cancelling circuit, which is connected with the second        trans-impedance amplifying circuit, and configured to cancel the        two amplified voltage signals and output cancelled voltage        signals.

In one embodiment, the ranging circuit is configured to control the biasvoltage applied to the photodetector so that it is smaller than thebreakdown voltage within a first preset time period between atransmitting time and an initial time, wherein the transmitting time isa transmitting time of a transmitted laser signal, the initial time isafter the receiving time of the stray reflected signal, and the firstpreset time period is a time period including the receiving time of thestray reflected signal.

In one embodiment, the ranging circuit is further configured to boostthe bias voltage applied to the photodetector within a second presettime period between the initial time and a first time, with a boostinggradient greater than a preset gradient, and the second preset timeperiod is a boosting time period of the bias voltage.

In one embodiment, the ranging circuit is further configured to: in athird preset time period between the first time and a second time,determine a value of a bias voltage corresponding to a current timeaccording to a preset correspondence relationship between a receivingtime of the reflected laser signal and the bias voltage, and control thebias voltage applied to the photodetector according to the value of thebias voltage corresponding to the current time, wherein the presetcorrespondence relationship between the receiving time of the reflectedlaser signal and the bias voltage is determined according to a presetcorrespondence relationship between a ranging flight time and a gain ofthe photodetector and a preset correspondence relationship between again of the photodetector and the bias voltage, and the third presettime period is a ranging time period.

In one embodiment, when the transmitted laser signal is a pulse signal,the ranging circuit is configured to output a control signal accordingto a predefined rule, and control a pulse bias voltage to be applied tothe photodetector through the control signal

In one embodiment, a preset flight time of the stray reflected signal isa statistical value of multiple measurement values of a flight time in aprocess in which the transmitted laser signal reaches the photodetectorthrough the stray light path other than the ranging light path.

In one embodiment, the apparatus further includes:

-   -   a power module, which is connected with the photodetector and        the power control circuit, respectively, and configured to        receive a control signal transmitted from the power control        circuit and apply a bias voltage corresponding to the control        signal to the photodetector.

In a second aspect, a lidar system includes a lidar transmittingapparatus configured to transmit a laser signal, and the above-mentionedlidar receiving apparatus.

In a third aspect, a laser ranging method includes:

-   -   transmitting a laser signal;    -   controlling a bias voltage of a photodetector according to a        predefined rule;    -   acquiring a current signal output from the photodetector when        the bias voltage of the photodetector is greater than a        breakdown voltage of the same, wherein the current signal is        correlated to a reflected laser signal corresponding to the        transmitted laser signal; and    -   calculating distance data according to the current signal,    -   wherein the predefined rule includes: at a receiving time of a        stray reflected signal, the bias voltage of the photodetector is        smaller than the breakdown voltage; and the receiving time of        the stray reflected signal is a time at which the transmitted        laser signal reaches the photodetector through a stray light        path other than a ranging light path, and is correlated to a        preset flight time of the stray reflected signal.

In one embodiment, the calculating the distance data according to thecurrent signal includes:

-   -   converting the current signal into a voltage signal and        amplifying the voltage signal to acquire an amplified voltage        signal; and    -   calculating distance data according to the amplified voltage        signal.

In one embodiment, the method further includes:

-   -   acquiring a current signal output from the reference        photodetector while acquiring a current signal output from the        photodetector, wherein the reference photodetector is in a        light-shielded state and associated with the photodetector, and        the current signal output from the reference photodetector is        positively correlated to the bias voltage of the reference        photodetector;    -   the calculating the distance data according to the current        signal includes:    -   performing cancellation and trans-impedance amplification on        both current signals output from the photodetector and the        reference photodetector, and outputting voltage signals obtained        after the cancellation and the trans-impedance amplification are        performed; and    -   calculating distance data according to the voltage signal        obtained after the cancellation and the trans-impedance        amplification are performed.

In a fourth aspect, a laser ranging controller includes a memory and aprocessor. The memory stores a computer program, and the processorimplements the following steps when executing the computer program:

-   -   transmitting a laser signal;    -   controlling a bias voltage of a photodetector according to a        predefined rule;    -   acquiring a current signal output from the photodetector when        the bias voltage of the photodetector is greater than a        breakdown voltage of the same, wherein the current signal is        correlated to a reflected laser signal corresponding to the        transmitted laser signal;    -   calculating distance data according to the current signal,    -   wherein the predefined rule includes: at a receiving time of the        stray reflected signal, the bias voltage of the photodetector is        smaller than the breakdown voltage;    -   and the receiving time of the stray reflected signal is a time        at which the transmitted laser signal reaches the photodetector        through a stray light path other than a ranging light path, and        is correlated to a preset flight time of the stray reflected        signal.

In a fifth aspect, a computer readable storage medium stores a computerprogram thereon, wherein the computer program implements the followingsteps when being executed by a processor:

-   -   transmitting a laser signal;    -   controlling a bias voltage of a photodetector according to a        predefined rule;    -   acquiring a current signal output from the photodetector when        the bias voltage of the photodetector is greater than a        breakdown voltage of the same, wherein the current signal is        correlated to a reflected laser signal corresponding to the        transmitted laser signal;    -   calculating distance data according to the current signal,    -   wherein the predefined rule includes: at a receiving time of a        stray reflected signal, the bias voltage of the photodetector is        smaller than the breakdown voltage; and the receiving time of        the stray reflected signal is a time at which the transmitted        laser signal reaches the photodetector through a stray light        path other than a ranging light path, and is correlated to a        preset flight time of the stray reflected signal.

In the lidar receiving apparatus, the lidar system, the laser rangingmethod, the laser ranging controller, and the computer readable storagemedium, at the receiving time of the stray reflected signal, the powercontrol circuit may control the bias voltage of the photodetector sothat it is smaller than the breakdown voltage, such that the strayreflected signal is unable to excite the photodetector, and there is noneed for recovery time for the photodetector. Even if the flight time ofthe reflected laser signal is short during near ranging, thephotodetector is in a normal working state and the bias voltage isgreater than the breakdown voltage; accordingly, the reflected lasersignal may excite the photodetector, and the photodetector generates acurrent signal corresponding to the reflected laser signal. Therefore,the ranging circuit may calculate the distance data according to thecurrent signal. The short-range blind area is reduced. It should beunderstood that the close-range blind area is theoretically an opticalpath length of the stray light path in the order of centimeters. As tothe entire system, in consideration of the optical path length from alaser transmitted portion to the entire casing, theoretically anon-blind detection area may be realized at a system level.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram showing an application environment of a lidarreceiving apparatus according to an embodiment;

FIG. 2 a is a block diagram showing a structure of a lidar receivingapparatus according to an embodiment;

FIG. 2 b is a schematic diagram showing a photodetector according to anembodiment;

FIG. 2 c is a curve showing a correspondence relationship between a gainand a bias voltage of a photodetector according to an embodiment;

FIG. 3 is a block diagram showing a structure of a lidar receivingapparatus according to an embodiment;

FIG. 4 is a block diagram showing a structure of a lidar receivingapparatus according to an embodiment;

FIG. 5 a is a first schematic diagram showing a cancelling andtrans-impedance amplifying circuit according to an embodiment;

FIG. 5 b is a second schematic diagram showing a cancelling andtrans-impedance amplifying circuit according to an embodiment;

FIG. 5 c is a third schematic diagram showing a cancelling andtrans-impedance amplifying circuit according to an embodiment;

FIG. 5 d is a fourth schematic diagram showing a cancelling andtrans-impedance amplifying circuit according to an embodiment;

FIG. 6 is a schematic diagram showing a power module according to anembodiment;

FIG. 7 is a schematic diagram showing a waveform of a bias voltage of aphotodetector according to an embodiment; and

FIG. 8 is a schematic flow diagram of a laser ranging method accordingto an embodiment.

DETAILED DESCRIPTION

In order to make the objective, the technical solution and theadvantages of the present application apparent, the present applicationwill be described in detail with reference to accompanying drawings andembodiments. It should be understood that specific embodiments describedherein are only for describing the present application, but not forlimiting the present application.

A lidar receiving apparatus provided in the present application may beapplied to a lidar system as shown in FIG. 1 . Among them, a lidartransmitting apparatus transmits a transmitted laser signal (light), andthe laser light is collimated by a collimator. The collimated laserlight enters a lens barrel and is split by a polarization splittingplane to obtain a laser light which is in a polarized state and istransmitted through the polarization splitting plane. The laser light isreflected by a first reflecting mirror to a MEMS (microelectromechanical system) mirror. A scanning frequency and a scanningdirection of the laser light are adjusted by the MEMS mirror to realizethe scanning of the target. A reflected laser signal reflected by thetarget is reflected to the first reflecting mirror. Meanwhile, thereflected laser signal is reflected to the polarization splitting planeby the first reflecting mirror. The reflected laser signal is reflectedto a filter by the polarization splitting plane. A clutter signal isfiltered out by the filter to acquire a filtered reflected laser signal.Meanwhile, the filtered reflected laser signal is reflected to areceiving lens by a second reflecting mirror. The reflected laser signalis detected and ranged by the lidar receiving apparatus to acquiredistance data.

However, in addition to the above-mentioned ranging optical path, due tolens impurities, vertical errors and parallel errors of the inner wallof a lens barrel, and the like, the transmitted laser signal may bereflected by the inner wall of the lens barrel to the lidar receivingapparatus, that is, may reach a photodetector along a stray light pathother than a ranging light path, wherein a signal in which thetransmitted laser signal reaches the photodetector along the stray lightpath may be referred to as the stray reflected signal. Due to a shortoptical path length of the stray reflected signal relative to thereflected laser signal, the photodetector in the traditional lidarreceiving apparatus will first detect the stray reflected signal, butthere is a recovery time after the photodetector detects the strayreflected signal, and the reflected laser signal cannot be detectedwithin the recovery time. During near ranging, due to short flight time,when the reflected laser signal reaches the photodetector, thephotodetector may still be within the recovery time, that is, may notdetect the reflected laser signal for a to-be-ranged target.Accordingly, a certain range of short-range blind areas may be caused.Correspondingly, the lidar receiving apparatus of this embodiment maysolve the above-mentioned problem of the short-range blind areas.

It should be noted that the lidar receiving apparatus of this embodimentmay be applied not only to a ranging system as shown in FIG. 1 describedabove, but also to other ranging systems. The lidar receiving apparatusmay perform ranging by adopting a polarized light or a common laserlight. In addition, the lidar receiving apparatus of this embodiment maybe applied to other lidar systems such as a vehicle-mounted lidar, andnot limited to the ranging system.

In one embodiment, as shown in FIG. 2 a , there is provided a lidarreceiving apparatus, which is described by taking an applicationenvironment in FIG. 1 as an example. The lidar receiving apparatus mayinclude:

-   -   a photodetector 11, which is configured to receive a reflected        laser signal, and to convert the reflected laser signal into a        current signal when a bias voltage of the photodetector is        greater than a breakdown voltage of the same;    -   a ranging circuit 12, which is connected with the photodetector,        and configured to calculate distance data according to the        current signal;    -   a power control circuit 13, which is connected with the        photodetector and configured to control the bias voltage applied        to the photodetector according to a predefined rule;    -   wherein the predefined rule includes: at a receiving time of a        stray reflected signal, the bias voltage of the photodetector is        smaller than the breakdown voltage; and the receiving time of        the stray reflected signal is a time at which the transmitted        laser signal reaches the photodetector through a stray light        path other than a ranging light path, and is correlated to a        preset flight time of the stray reflected signal

With reference to FIG. 2 b , a high-sensitivity SiPM (siliconphotomultiplier) serves as an example of photodetector. The SiPM iscomposed of a plurality of microcells connected in parallel, and eachmicrocell is composed of an avalanche diode (APD) and a quenchingresistor. When a bias voltage (generally, a reverse bias voltage, tensof volts) is applied to the SiPM, a depletion layer of the APD of eachmicrocell has a high-intensity electric field. At this time, if there isa photon from the outside, Compton scattering occurs with electron-holepairs in a semiconductor to eject electrons or holes. Then, thehigh-energy electrons and holes are accelerated in an electric field toeject a large number of secondary electrons and holes, that is, anavalanche effect occurs. At this time, a current output from eachmicrocell suddenly increases, a voltage on the quenching resistor alsoincreases, while the electric field in the APD decreasesinstantaneously, that is, an avalanche stops after the APD outputs atransient current pulse. Accordingly, an APD array may serve as aphotodetector to convert a light signal into a current signal.

In particular, the SiPM has the following basic characteristics.

A. A photoelectric amplification capability (that is, gain) of the SiPMis positively correlated to a bias voltage. FIG. 2 c is a curve showingcorrespondence relationship between gains and bias voltages of SiPMswith different specifications. It may be seen that if a differencebetween the bias voltage and the breakdown voltage (a characteristic ofthe SiPM) is called an overvoltage, it may be found that the gain is indirect proportion to the overvoltage within a certain range. The smallerthe overvoltage is, the smaller a photoelectric amplification factor is.When the overvoltage is close to or smaller than 0V, that is, when thebias voltage is smaller than the breakdown voltage, the gain is close tozero, that is, no avalanche effect occurs in the SiPM.

B. When there is an incident photon, the incident photon may beeffectively absorbed by a large number of avalanche diodes and excitesthe avalanche effect, thereby making the large number of avalanchediodes conduct and output pulse currents. Thereafter, there is a needfor charging equivalent capacitors C_(cell) at two ends of each of theavalanche diodes (because each avalanche diode is connected in parallelwith one equivalent capacitor due to the structure of the SiPM), suchthat charging the equivalent capacitors of the avalanche diodes iscompleted. Accordingly, the SiPM returns to a normal bias state. Beforecharging the equivalent capacitors is completed, the SiPM is difficultto effectively detect an incident light and output a current. Amongthem, the equivalent capacitor C_(cell) and the quenching resistor R qdetermine a recovery time constant of the microcell, and a time it taketo recover to 90% of a bias voltage is about 2.3 times the recovery timeconstant, that is, the recovery time may be:

T _(recovery)=2.3×R _(q) ×C _(cell)

In this embodiment, the lidar receiving apparatus may supply a power tothe photodetector with an external power supply, that is, to apply abias voltage. Accordingly, a power control circuit may control theexternal power supply to apply the bias voltage to the photodetectoraccording to a predefined rule.

As shown in FIG. 2 b , the photodetector includes a decoupling circuitand a readout circuit in addition to a photodetector such as a SiPM,wherein the decoupling circuit includes a decoupling capacitor C, whichis located between a bias voltage applying end of the photodetector andground (such as a casing) and configured to remove a power supply noiseand stabilize the bias voltage; and the readout circuit includes aresistor R s, which is configured to convert a current signal into avoltage signal that is easy to measure. S out and F_(out) are adirect-current coupling output terminal and an alternating-currentcoupling output terminal, respectively. In this embodiment, the outputof the photodetector may be read out by employing thealternating-current coupling output terminal.

It should be noted that the receiving time of the stray reflected signalis a time at which the transmitted laser signal reaches thephotodetector through a stray light path other than the ranging lightpath and is correlated to the preset flight time of the stray reflectedsignal, wherein the preset flight time of the stray reflected signal maybe obtained by measuring a time it takes for the transmitted lasersignal to reach the photodetector through the stray light path otherthan the ranging light path. Accordingly, the receiving time of thestray reflected signal may be a sum of the laser transmitting time andthe preset flight time of the stray reflected signal, which isessentially a predicted receiving time of the stray reflected signal,because the actual receiving time of the stray reflected signal may notbe detected during actual ranging.

Since the bias voltage of the photodetector is smaller than thebreakdown voltage at the receiving time of the stray reflected signal,the stray reflected signal is unable to excite the photodetector, andthere is no need for recovery time for the photodetector. Accordingly,when the reflected laser signal reaches the photodetector, thephotodetector is in a normal working state, and the bias voltage isgreater than the breakdown voltage. Therefore, the photodetector maygenerate a current signal corresponding to the reflected laser signal.Accordingly, the ranging circuit may calculate distance data accordingto the current signal.

Particularly, the ranging circuit may analyze the current signalcorresponding to the reflected laser signal to obtain distance data,that is, a to-be-ranged distance, wherein the to-be-ranged distance iscalculated according to the optical path length, as shown in thefollowing formula:

D=0.15m/ns×T

-   -   wherein T is flight time of the reflected laser signal in ns        (nanosecond).

It should be understood that the difference between the time at whichthe ranging circuit detects the current signal corresponding to thereflected laser signal and the laser transmitting time may serve as theflight time of the reflected laser signal, so that the to-be-rangeddistance may be calculated according to the flight time of the reflectedlaser signal.

In the lidar receiving apparatus of this embodiment, at the receivingtime of the stray reflected signal, the power control circuit maycontrol the bias voltage of the photodetector so that it is smaller thanthe breakdown voltage, such that the stray reflected signal is unable toexcite the photodetector, and there is no need for recovery time for thephotodetector. Even if the flight time of the reflected laser signal isshort during near ranging, the photodetector is in a normal workingstate and the bias voltage is greater than the breakdown voltage. Thereflected laser signal may excite the photodetector, and thephotodetector generates a current signal corresponding to the reflectedlaser signal. Therefore, the ranging circuit may calculate the distancedata according to the current signal. The short-range blind area isdecreased. It should be understood that the close-range blind area istheoretically an optical path length of the stray light path in theorder of centimeters. However, on the entire system, the optical pathlength from a laser transmitted portion to the entire casing isconsidered, and non-blind detection area may be theoretically realizedat a system level.

In one embodiment, as shown in FIG. 3 , there is provided with astructure of a ranging circuit. Particularly, the ranging circuit 12 mayinclude:

-   -   a trans-impedance amplifying circuit 121, which is connected        with the photodetector 11, and configured to convert a current        signal into a voltage signal and amplify the voltage signal to        acquire an amplified voltage signal; and    -   a first processing circuit 122, which is connected with the        trans-impedance amplifying circuit 121, and configured to        control a bias voltage applied to the photodetector 11 according        to a predefined rule, and calculate distance data according to        the amplified voltage signal.

It should be understood that a current signal generated by thephotodetector according to the reflected laser signal is weak, and thereis a need for converting the current signal into a voltage signal andamplifying the voltage signal by the trans-impedance amplifying circuitto be processed by the first processing circuit.

It should be noted that, in the absence of light, when the applied biasvoltage is greater than the breakdown voltage, the SiPM will output acurrent signal, the current signal is positively correlated to the biasvoltage and its duration is approximately the same as the recovery timeof the microcell. For ease of differentiation, a current signalresulting from the reflected laser signal is called a photocurrentsignal, and a corresponding voltage signal is called a photovoltagesignal. A current signal resulting from the bias voltage (actually, anovervoltage) is called a bias current signal, and a correspondingvoltage signal is called a bias voltage signal. Therefore, the voltagesignal obtained by the first processing circuit may only include thebias voltage signal at most times; and at a time at which the reflectedlaser signal reaches the photodetector, the voltage signal includes thebias voltage signal and the photovoltage signal.

It may be seen that when the reflected laser signal reaches thephotodetector, the voltage signal received by the first processingcircuit will suddenly increase. Therefore, for example, the firstprocessing circuit may calculate a voltage gradient of the voltagesignal according to the received voltage signal. When the voltagegradient of the voltage signal is greater than a preset gradientthreshold, it is determined that the voltage signal at this timeincludes a photovoltage signal, that is, this time is a time at whichthe reflected laser signal reaches the photodetector, so that the flighttime of the reflected laser signal may be calculated according to thetime at which the reflected laser signal reaches the detectionphotoelectric signal and the laser transmitting time, and further theto-be-ranged distance is calculated.

In some embodiments, the first processing circuit may detect thephotovoltage signal by employing other signal processing methods, so asto determine the time at which the reflected laser signal reaches thephotodetector, which is not limited in this embodiment.

However, in general, a photocurrent signal is weaker than a bias currentsignal, and there might even be a difference of an order of magnitudebetween the intensity of the photocurrent signal and that of the biascurrent signal. As such, it is difficult for the ranging circuit todetect the photocurrent signal or the photovoltage signal. Accordingly,with reference to FIG. 4 , based on the lidar receiving apparatus shownin FIG. 2 a , the lidar receiving apparatus of this embodiment mayfurther include a reference photodetector 14, wherein the referencephotodetector 14 is in a light-shielded state, and is connected inparallel with the photodetector 11;

-   -   the ranging circuit 12 may include:    -   a cancelling and trans-impedance amplifying circuit 123, which        is connected with the photodetector 11 and the reference        photodetector 14, respectively, and configured to perform        cancellation and trans-impedance amplification on both current        signals output from the photodetector 11 and the reference        photodetector 14 and output voltage signals obtained after the        cancellation and the trans-impedance amplification are        performed, wherein the current signal output from the reference        photodetector 14 is positively correlated to the bias voltage        applied to the reference photodetector 14; and    -   a second processing circuit 124, which is connected with the        cancelling and trans-impedance amplifying circuit 123, and        configured to control the bias voltage applied to the        photodetector 11 according to the predefined rule, and calculate        the distance data according to the voltage signals obtained        after the cancellation and the trans-impedance amplification are        performed.

It should be understood that, because the reference photodetector isconnected in parallel with the photodetector, the bias voltage of thereference photodetector is equal to that of the photodetector, that is,the bias current signals of the reference photodetector and thephotodetector are the same. Meanwhile, because the referencephotodetector is in the light-shielded state, the current signal outputfrom the reference photodetector is a bias current signal at any time.Therefore, the voltage signal obtained after the cancellation and thetrans-impedance amplification are performed has been cancelled, and abias voltage signal component thereof is removed, only leaving thephotovoltage signal component. Therefore, the voltage signal obtainedafter the cancellation and the trans-impedance amplification areperformed is a photovoltage signal at the time at which the reflectedlaser signal reaches the photodetector, and should be 0 other than thetime at which the reflected laser signal reaches the detectionphotoelectric signal. Therefore, the second processing circuit maysensitively detect the voltage signal obtained after the cancellationand the trans-impedance amplification are performed, and the time ofdetecting the voltage signal obtained after the cancellation and thetrans-impedance amplification are performed serves as the time at whichthe reflected laser signal reaches the photodetector. Accordingly, thesensitivity and the accuracy of detecting the reflected laser signal areimproved, and the ranging accuracy is increased.

In one embodiment, the cancelling and trans-impedance amplifying circuit123 may include:

-   -   a first cancelling circuit, which is connected with the        photodetector and the reference photodetector, respectively, and        configured to cancel both current signals output from the        photodetector and the reference photodetector and output        cancelled current signals;    -   a first trans-impedance amplifying circuit, which is connected        with the first cancelling circuit, and configured to convert the        cancelled current signals into voltage signals and amplify the        voltage signals to acquire amplified voltage signals.

In another embodiment, the cancelling and trans-impedance amplifyingcircuit may include:

-   -   a second trans-impedance amplifying circuit, which is connected        with the photodetector and the reference photodetector,        respectively, and configured to convert both current signals        output from the photodetector and the reference photodetector        into voltage signals, respectively, and amplify the voltage        signals to acquire two amplified voltage signals; and    -   a second cancelling circuit, which is connected with the second        trans-impedance amplifying circuit, and configured to cancel the        two amplified voltage signals and output cancelled voltage        signals.

It should be noted that there are at least two ways to implement thecancelling and trans-impedance amplifying circuit: one is to firstlyperform current subtraction and then perform trans-impedanceamplification, that is, the first embodiment described above; the otheris to firstly perform trans-impedance amplification and then performvoltage subtraction, that is, the second embodiment described above.Since the second embodiment will limit an effective dynamic range of asignal link and increase the power consumption and the cost, the presentapplication implements the cancelling and trans-impedance amplifyingcircuit by employing the first embodiment, wherein the first cancellingcircuit may be a balun transformer, and the first trans-impedanceamplifying circuit may be a trans-impedance amplifier.

FIG. 5 a shows an embodiment of a cancelling and trans-impedanceamplifying circuit. Current signals output from sensor A (aphotodetector) and sensor B (a reference photodetector) are input toboth ends of a balancing side of the balun transformer, respectively. Acurrent remained after cancellation is performed is coupled to a primaryside through a transformer. Then the current signals are input to thetrans-impedance amplifier for trans-impedance amplification to acquirevoltage signals subjected to trans-impedance amplification.Particularly, in this embodiment, a balun transformer with low insertionloss and high symmetry may be selected, that is, a balun transformerwith small signal attenuation and good cancellation performance.Therefore, a photocurrent signal range close to the output of a singlephotodetector may be obtained. In terms of the noise, a thermal noise ofa matching resistor RT is mainly added, and is much smaller than acurrent noise of the trans-impedance amplifying circuit itself (thenoise exists in a trans-impedance amplification process). The influenceof the noise on a signal-to-noise ratio of the photocurrent signal maybe basically ignored. That is, only the extremely small thermal noise isadded. However, the photocurrent signal is hardly weakened, and theinfluence on the signal-to-noise ratio is small. Therefore, thephotocurrent signal amplification capability of the circuit is hardlyreduced.

FIG. 5 b shows an embodiment of a cancelling and trans-impedanceamplifying circuit. A structure of the cancelling and trans-impedanceamplifying circuit is basically the same as that shown in FIG. 5 b , butonly one sensor A is used. A cancellation signal output from thereference photodetector is realized by a passive circuit (a sensorequivalent circuit). The sensor equivalent circuit may achieve an outputcharacteristic equivalent to the reference photodetector in alight-shielded state under a bias voltage controlled by the powercontrol circuit.

FIG. 5 c shows an embodiment of a cancelling and trans-impedanceamplifying circuit. Current signals output from sensor A (aphotodetector) and sensor B (a reference photodetector) are respectivelyinput to a trans-impedance amplifier for primary amplification. Thetrans-impedance amplifier outputs amplified voltage signals. The twoamplified voltage signals are input to a subtractor, which outputs thecanceled voltage signals. Then, secondary amplification is performed onthe canceled voltage signals.

FIG. 5 d shows an embodiment of a cancelling and trans-impedanceamplifying circuit. A structure of the cancelling and trans-impedanceamplifying circuit is basically the same as that shown in FIG. 5 c , butonly one sensor A is used. A cancellation signal output from thereference photodetector is implemented by a passive circuit (a sensorequivalent circuit) as well.

For the comparison of the four cancelling and trans-impedance amplifyingcircuits described above, there is a need for the obvious problem in thelatter two solutions to use two trans-impedance amplifiers. Moreover,after the primary trans-impedance amplification is performed, in orderto limit amplitude unsaturation of a primary output signal, thetrans-impedance gain will be reduced, and there is a need foradditionally increasing an amplification stage, which not only increasesthe power consumption, but also increases the cost. For the firstcircuit, the design requirements may be met. However, the cost isincreased because the two sensors are used. For the second circuit,better advantages in cost and power consumption are obtained since onlyone sensor is used.

With reference to FIG. 4 , the lidar receiving apparatus may furtherinclude:

-   -   a power module 15, which is connected with the photodetector 11        and the power control circuit 13, respectively, and configured        to receive a control signal transmitted from the power control        circuit 13 and apply a bias voltage corresponding to the control        signal to the photodetector 11. It should be understood that        when the reference photodetector is connected in parallel with        the photodetector, the power module applies the bias voltage to        the reference photodetector while applying the same bias voltage        to the photodetector. The power module is integrated in a lidar        receiving apparatus, which may make the lidar receiving        apparatus more compact and the way of supplying power more        convenient.

As shown in FIG. 6 , the power module may include a digital-to-analogconverter, an amplifying and conditioning device and an output driverwhich are connected in sequence. The digital-to-analog converter isconfigured to receive a digital control signal transmitted by a powercontrol circuit and to convert the digital control signal into an analogcontrol signal, wherein the analog control signal is a voltage controlsignal, for example, a voltage waveform signal of 0 to 1V. Theamplifying and conditioning device is configured to amplify andcondition the voltage control signal (such as an up and down movement ofthe voltage control signal to adjust an amplitude range). The outputdriver may be a power amplifier, which may amplify the amplified andconditioned voltage control signal and output it to the photodetector,that is, to output a bias voltage. The power module may achieve precisecontrol of the bias voltage in time and amplitude by matching thehigh-speed digital-to-analog converter with the output driver with ahigh driving capability.

In one embodiment, FIG. 7 shows a schematic diagram showing a waveformfor detecting a bias voltage of a photodetector and represents apredefined rule for controlling the bias voltage by a power controlcircuit. Particularly, the predefined rule may include: the powercontrol circuit controls the bias voltage applied to the photodetectorso that it is smaller than a breakdown voltage of the same within afirst preset time period between a transmitting time and an initialtime, wherein the transmitting time is a transmitting time of atransmitted laser signal, the initial time is after the receiving timeof the stray reflected signal, and the first preset time period is atime period including the receiving time of the stray reflected signal.

In some embodiments, the power control circuit is further configured toboost the bias voltage applied to the photodetector within a secondpreset time period between the initial time and a first time, with aboosting gradient greater than a preset gradient, and the second presettime period is a boosting time period of the bias voltage.

In some embodiments, the ranging circuit is further configured to: in athird preset time period between the first time and a second time,determine a value of a bias voltage corresponding to a current timeaccording to a preset correspondence relationship between a receivingtime of the reflected laser signal and the bias voltage, and control thebias voltage applied to the photodetector according to the value of thebias voltage corresponding to the current time, wherein the presetcorrespondence relationship between the receiving time of the reflectedlaser signal and the bias voltage is determined according to a presetcorrespondence relationship between a ranging flight time and a gain ofthe photodetector and a preset correspondence relationship between again of the photodetector and the bias voltage, and the third presettime period is a ranging time period.

With reference to FIG. 7 , the laser transmitting time may be a T=0time, the initial time is T_(br), and the initial time is after thereceiving time of the stray reflected signal. so as to be within thefirst preset time period from 0 to T_(br), the bias voltage is smallerthan the breakdown voltage V_(br), and the photoelectric amplificationgain is approximately zero. Accordingly, a stray reflected signal isprevented from exciting the photodetector.

During the second preset time period from T_(br) to T₁, the bias voltageboosts rapidly, and the boosting gradient is higher than 1V/ns, so thata photoelectric amplification factor of the photodetector is rapidlyincreased to ensure that the photodetector may sufficiently effectivelyamplify a real reflected laser signal after the stray reflected signalwithin the third preset time period, so as to be detected. In order toboost the bias voltage as soon as possible, the bias voltage at theT_(br) time may be V_(br). The duration of the second preset time periodmay be reduced.

During the third preset time period from T₁ to T₃, the lidar receivingapparatus may sufficiently and effectively amplify the reflected lasersignal. During near ranging, the reflected laser signal has a shortflight time and high intensity, so that the requirement for the gain islow and the reflected laser signal is prevented from beingoversaturated. During remote ranging, the reflected laser signal has along flight time and low intensity; therefore, a high gain is requiredso as to refrain from failing to detect the reflected laser signal.Therefore, the correspondence relationship between the flight time ofthe reflected laser signal and the bias voltage may be determinedaccording to the preset correspondence relationship between a rangingflight time and the gain of the photodetector and the presetcorrespondence relationship between a gain of the photodetector and thebias voltage. Further, the correspondence relationship between thereceiving time of the reflected laser signal and the bias voltage may bedetermined according to the laser transmitting time.

The preset correspondence relationship between the ranging flight timeand the gain of the photodetector may be determined according to thegains required by reflected laser signal intensities corresponding todifferent ranging flight times. The preset correspondence relationshipbetween the gain of the photodetector and the bias voltage may bedetermined according to the gain of the photodetector under measureddifferent bias voltages.

It should be understood that the first preset time period is determinedwith respect to the laser transmitting time and the initial time. Theinitial time is related to the receiving time of the stray reflectedsignal. If the receiving time of the stray reflected signal is highenough in accuracy and is high enough in confidence, the initial timemay be equal to the receiving time of the stray reflected signal.Generally, there is a need for setting a safety time period between thereceiving time of the stray reflected signal and the initial time. Thesecond preset time period is related to the initial time and the firsttime, and is actually related to the boosting capability of the powermodule to the bias voltage. The faster the boosting gradient is, theshorter the second preset time period is. In a case of a certainboosting capability of the bias voltage, the first time is correlated tothe shortest effective ranging distance. When the shortest effectiveranging distance is measured, the reflected laser signal may beeffectively amplified, so that the current signal corresponding to thereflected laser signal may be detected. The third preset time period iscorrelated to the first time and the second time, and the second time iscorrelated to the longest effective ranging distance. When theto-be-ranged distance is longer, the reflected laser signal intensity isextremely low, and thus a greater gain, a more sensitive photodetectorand a more accurate signal processing algorithm are required.

A bias voltage control rule of this embodiment suppresses the strayreflected signal of the stray light path on the one hand, and implementstime gain control on the other hand. An amplification factor of thephotodetector is limited by changing the bias voltage at differenttimes, so that the reflected laser signal is prevented from beingsaturated and the ranging accuracy is ensured.

In one embodiment, when the transmitted laser signal is a pulse signal,the power control circuit is configured to output a control signalaccording to a predefined rule, and control the application of a pulsebias voltage to the photodetector through the control signal. Certainly,this embodiment is not limited to a continuous laser signal or a pulsedlaser signal. The pulsed laser signal is relatively high in power, sothat the longest effective ranging distance may be increased and theranging range may be increased. It should be understood that the pulsesignal has a certain period. In each period, the control of the powercontrol circuit of this embodiment on the bias voltage may refer to theabove description.

In one embodiment, the preset flight time of the stray reflected signalis a statistical value of multiple measured values of the flight time inthe process in which the transmitted laser signal reaches thephotodetector through the stray light path other than the ranging lightpath. In some embodiments, the statistical value of the multiplemeasurement values of the flight time may be the maximum value of themultiple measurement values, because the bias voltage is generallycontrolled to be smaller than the breakdown voltage before the predictedreceiving time of the stray reflected signal, so that it is possible tomake the predicted receiving time of the stray reflected signal as largeas possible within a certain confidence range, and ensure the realreceiving time of the stray reflected signal is before the predictedreceiving time of the stray reflected signal as much as possible, so asto ensure that the bias voltage at the real receiving time of the strayreflected signal is smaller than the breakdown voltage and improve thestability.

In addition, this embodiment further provides a lidar system, whichincludes a lidar transmitting apparatus configured to transmit a lasersignal, and the above-mentioned lidar receiving apparatus.Theoretically, the lidar system of this embodiment may realize anon-blind detection area.

With reference to FIG. 8 , this embodiment further provides a laserranging method, which may include:

-   -   S801: transmitting a laser signal;    -   S802: controlling a bias voltage of a photodetector according to        a predefined rule;    -   S803: acquiring a current signal output from the photodetector        when the bias voltage of the photodetector is greater than a        breakdown voltage of the same, wherein the current signal is        correlated to a reflected laser signal corresponding to the        transmitted laser signal; and    -   S804: calculating distance data according to the current signal,    -   wherein the predefined rule includes: at a receiving time of a        stray reflected signal, the bias voltage of the photodetector is        smaller than the breakdown voltage; and the receiving time of        the stray reflected signal is a time at which the transmitted        laser signal reaches the photodetector through a stray light        path other than a ranging light path, and is correlated to a        preset flight time of the stray reflected signal.

The laser ranging method of this embodiment may be applied in a lidarsystem. At the receiving time of the stray reflected signal, acontroller of the lidar system may control the bias voltage of thephotodetector so that it is smaller than the breakdown voltage, and thestray reflected signal is unable to excite the photodetector, and thereis no need for recovery time for the photodetector. Even if the flighttime of the reflected laser signal is short during near ranging, thephotodetector is in a normal working state and the bias voltage isgreater than the breakdown voltage, as such, the reflected laser signalmay excite the photodetector, and the photodetector generates a currentsignal corresponding to the reflected laser signal. The reflected lasersignal after the stray reflected signal may be effectively detected.Therefore, the controller of the lidar system may calculate the distancedata according to the current signal. A short-range blind area isdecreased.

In one embodiment, S804 may include: converting the current signal intoa voltage signal and amplifying the voltage signal to acquire anamplified voltage signal; and calculating distance data according to theamplified voltage signal.

In another embodiment, the method may further include: acquiring acurrent signal output from a reference photodetector while acquiring acurrent signal output from the photodetector, wherein the referencephotodetector is in a light-shielded state and is associated with thephotodetector, and the current signal output from the referencephotodetector is positively correlated to the bias voltage of thereference photodetector. S804 may include: performing cancellation andtrans-impedance amplification on both current signals output from thephotodetector and the reference photodetector, and outputting voltagesignals obtained after the cancellation and the trans-impedanceamplification are performed; and calculating distance data according tothe voltage signals obtained after the cancellation and thetrans-impedance amplification are performed.

For a specific description of the laser ranging method, reference ismade to the foregoing description of the lidar receiving apparatus, anddetails will be omitted here.

In one embodiment, a laser ranging controller includes a memory and aprocessor. The memory stores a computer program, and the processorimplements the following steps when executing the computer program:

-   -   transmitting a laser signal;    -   controlling a bias voltage of a photodetector according to a        predefined rule;    -   acquiring a current signal output from the photodetector when        the bias voltage of the photodetector is greater than a        breakdown voltage of the same, wherein the current signal is        correlated to a reflected laser signal corresponding to the        transmitted laser signal; and    -   calculating distance data according to the current signal,    -   wherein the predefined rule includes: at a receiving time of the        stray reflected signal, the bias voltage of the photodetector is        smaller than the breakdown voltage;    -   and the receiving time of the stray reflected signal is a time        at which the transmitted laser signal reaches the photodetector        through a stray light path other than a ranging light path, and        is correlated to a preset flight time of the stray reflected        signal.

In one embodiment, a computer readable storage medium stores a computerprogram thereon, wherein the computer program implements the followingsteps when being executed by a processor:

-   -   transmitting a laser signal;    -   controlling a bias voltage of a photodetector according to a        predefined rule;    -   acquiring a current signal output from the photodetector when        the bias voltage of the photodetector is greater than a        breakdown voltage of the same, wherein the current signal is        correlated to a reflected laser signal corresponding to the        transmitted laser signal; and    -   calculating distance data according to the current signal,    -   wherein the predefined rule includes: the bias voltage of the        photodetector is smaller than the breakdown voltage at a        receiving time of the stray reflected signal; and the receiving        time of the stray reflected signal is a time at which the        transmitted laser signal reaches the photodetector through a        stray light path other than a ranging light path, and is        correlated to a preset flight time of the stray reflected        signal.

The technical features of the above embodiments may be arbitrarilycombined. In order to make the description concise, all possiblecombinations of the technical features in the above embodiments have notbeen described. However, if there is no contradiction in thecombinations of these technical features, these combinations should beconsidered to be the range described in this specification.

Although description of some implementations of the present applicationis presented in the embodiments above, the description should not beunderstood as limiting the protection scope of the present application.It should be noted that, various modifications and improvements may bemade by those skilled in the art without departure from the concept ofthe present application, and would fall within the protective scope ofthe present application. As such, the protection scope of the presentapplication should be limited only by the appended claims.

1. A lidar receiving apparatus, comprising: a photodetector, which isconfigured to receive a reflected laser signal and to convert thereflected laser signal into a current signal when a bias voltage of thephotodetector is greater than a breakdown voltage of the same; a rangingcircuit, which is connected with the photodetector, and configured tocalculate distance data according to the current signal; and a powercontrol circuit, which is connected with the photodetector, andconfigured to control the bias voltage applied to the photodetectoraccording to a predefined rule, wherein the predefined rule comprises:at a receiving time of a stray reflected signal, the bias voltage of thephotodetector is smaller than the breakdown voltage; and the receivingtime of the stray reflected signal is a time at which a transmittedlaser signal reaches the photodetector through a stray light path otherthan a ranging light path, and is correlated to a preset flight time ofthe stray reflected signal.
 2. The lidar receiving apparatus accordingto claim 1, wherein the ranging circuit comprises: a trans-impedanceamplifying circuit, which is connected with the photodetector, andconfigured to convert the current signal into a voltage signal andamplify the voltage signal to acquire an amplified voltage signal; and afirst processing circuit, which is connected with the trans-impedanceamplifying circuit, and configured to calculate distance data accordingto the amplified voltage signal.
 3. The lidar receiving apparatusaccording to claim 1, further comprising a reference photodetector,wherein the reference photodetector is in a light-shielded state, and isconnected in parallel with the photodetector; wherein the rangingcircuit comprises: a cancelling and trans-impedance amplifying circuit,which is connected with the photodetector and the referencephotodetector, respectively, and configured to perform cancellation andtrans-impedance amplification on both current signals output from thephotodetector and the reference photodetector, and output voltagesignals obtained after the cancellation and the trans-impedanceamplification are performed, wherein the current signal output from thereference photodetector is positively correlated to the bias voltageapplied to the reference photodetector; and a second processing circuit,which is connected with the cancelling and trans-impedance amplifyingcircuit, and configured to calculate the distance data according to thevoltage signals obtained after the cancellation and the trans-impedanceamplification are performed.
 4. The lidar receiving apparatus accordingto claim 3, wherein the cancelling and trans-impedance amplifyingcircuit comprises: a first cancelling circuit, which is connected withthe photodetector and the reference photodetector, respectively, andconfigured to cancel both current signals output from the photodetectorand the reference photodetector and output cancelled current signals;and a first trans-impedance amplifying circuit, which is connected withthe first cancelling circuit, and configured to convert the cancelledcurrent signals into voltage signals and amplify the voltage signals toacquire amplified voltage signals.
 5. The lidar receiving apparatusaccording to claim 3, wherein the cancelling and trans-impedanceamplifying circuit comprises: a second trans-impedance amplifyingcircuit, which is connected with the photodetector and the referencephotodetector, respectively, and configured to convert both currentsignals output from the photodetector and the reference photodetectorinto voltage signals, respectively, and amplify the voltage signals toacquire two amplified voltage signals; and a second cancelling circuit,which is connected with the second trans-impedance amplifying circuit,and configured to cancel the two amplified voltage signals and outputcancelled voltage signals.
 6. The lidar receiving apparatus according toclaim 1, wherein the power control circuit is configured to control thebias voltage applied to the photodetector so that it is smaller than thebreakdown voltage within a first preset time period between atransmitting time and an initial time, wherein the transmitting time isa transmitting time of a transmitted laser signal, the initial time isafter the receiving time of the stray reflected signal, and the firstpreset time period is a time period including the receiving time of thestray reflected signal.
 7. The lidar receiving apparatus according toclaim 6, wherein the power control circuit is further configured toboost the bias voltage applied to the photodetector within a secondpreset time period between the initial time and a first time, with aboosting gradient greater than a preset gradient, and the second presettime period is a boosting time period of the bias voltage.
 8. The lidarreceiving apparatus according to claim 7, wherein the power controlcircuit is further configured to: in a third preset time period betweenthe first time and a second time, determine a value of the bias voltagecorresponding to a current time according to a preset correspondencerelationship between a receiving time of the reflected laser signal andthe bias voltage, and control the bias voltage applied to thephotodetector according to the value of the bias voltage correspondingto the current time, wherein the preset correspondence relationshipbetween the receiving time of the reflected laser signal and the biasvoltage is determined according to a preset correspondence relationshipbetween a ranging flight time and a gain of the photodetector and apreset correspondence relationship between a gain of the photodetectorand the bias voltage, and the third preset time period is a ranging timeperiod.
 9. The lidar receiving apparatus according to claim 1, whereinwhen the transmitted laser signal is a pulse signal, the power controlcircuit is configured to output a control signal according to apredefined rule, and control a pulse bias voltage to be applied to thephotodetector through the control signal.
 10. The lidar receivingapparatus according to claim 1, wherein the preset flight time of thestray reflected signal is a statistical value of multiple measurementvalues of a flight time in a process in which a transmitted laser signalreaches the photodetector through a stray light path other than aranging light path.
 11. A lidar system, comprising: a lidar transmittingapparatus configured to transmit a laser signal, and the lidar receivingapparatus according to claim
 1. 12. A laser ranging method, comprising:transmitting a laser signal; controlling a bias voltage of aphotodetector according to a predefined rule; acquiring a current signaloutput from the photodetector when the bias voltage of the photodetectoris greater than a breakdown voltage of the same, wherein the currentsignal is correlated to a reflected laser signal corresponding to thetransmitted laser signal; and calculating distance data according to thecurrent signal, wherein the predefined rule comprises: at a receivingtime of a stray reflected signal, the bias voltage of the photodetectoris smaller than the breakdown voltage; and the receiving time of thestray reflected signal is a time at which the transmitted laser signalreaches the photodetector through a stray light path other than aranging light path, and is correlated to a preset flight time of thestray reflected signal.